NASA Spacecraft Galileo Reveals Magma Ocean Under Jupiter Moon
By Steve Hall
May 13, 2011 - New data analysis from NASA's Galileo
spacecraft reveals a subsurface ocean of molten or
partially molten magma beneath the surface of Jupiter's
volcanic moon Io. The finding heralds the first direct
confirmation of this kind of magma layer at Io and
explains why the moon is the most volcanic object known
in the solar system.
The research was conducted by scientists at the
University of California, Los Angeles, the University of
California, Santa Cruz, and the University of Michigan.
The study is published this week in the journal Science.
"Scientists are excited we finally understand where Io's magma is coming from and have an explanation for some of the mysterious signatures we saw in some of the Galileo's magnetic field data," said Krishan Khurana, lead author of the study and former co-investigator on Galileo's magnetometer team at UCLA.
"It turns out Io was continually giving off a 'sounding signal' in Jupiter's rotating magnetic field that matched what would be expected from molten or partially molten rocks deep beneath the surface." Io produces about 100 times more lava each year than all the volcanoes on Earth.
Earth's volcanoes occur in localized hotspots like the "Ring of
Fire" around the Pacific Ocean, Io's volcanoes are distributed
all over its surface. A global magma ocean about 20 to 30 miles
(30 to 50 kilometers) beneath Io's crust helps explain the
"It has been suggested that both the Earth and its moon may have
had similar magma oceans billions of years ago at the time of
their formation, but they have long since cooled," said Torrence
Johnson, a former Galileo project scientist based at NASA's Jet
Propulsion Laboratory (JPL) in Pasadena, Calif. He was not
directly involved in the study. "Io's volcanism informs us how
volcanoes work and provides a window in time to styles of
volcanic activity that may have occurred on the Earth and moon
during their earliest history."
NASA's Voyager spacecraft discovered Io's volcanoes in 1979, making that moon the only body in the solar system other than Earth known to have active magma volcanoes. The energy for the volcanic activity comes from the squeezing and stretching of the moon by Jupiter's gravity as Io orbits the largest planet in the solar system.
Galileo was launched in 1989 and began orbiting Jupiter in 1995.
Unexplained signatures appeared in magnetic field data from Galileo
flybys of Io in October 1999 and February 2000. After a successful
mission, the spacecraft intentionally was sent into Jupiter's atmosphere
"During the final phase of the Galileo mission, models of the
interaction between Io and Jupiter's immense magnetic field, which
bathes the moon in charged particles, were not yet sophisticated enough
for us to understand what was going on in Io's interior," said Xianzhe
Jia, a co-author of the study at the University of Michigan.
Recent work in mineral physics showed that a group of rocks known as "ultramafic" rocks become capable of carrying substantial electrical current when melted. Ultramafic rocks are igneous in origin, or form through the cooling of magma. On Earth, they are believed to originate from the mantle. The finding led Khurana and colleagues to test the hypothesis that the strange signature was produced by current flowing in a molten or partially molten layer of this kind of rock.
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